1. Field of the Invention
The present invention relates to a driving force transmission system to be applied to a transmission, transfer or differential of a vehicle.
2. Related Art
Generally in the driving force transmission system of the vehicle, there are arranged a plurality of rotary members, through which the output of an engine is transmitted to wheels. When a clutch mechanism is arranged in the driving force transmission system between the rotary members, on the other hand, the transmission/interruption of a torque can be arbitrarily switched by applying/releasing the clutch mechanism, if necessary. One example of the driving force transmission system in which the clutch mechanism is arranged in the torque transmission path of the rotary members is disclosed in Japanese Patent Laid-Open No. 282019/1991 (JP-A-3-282019).
The driving force transmission system, as disclosed, is equipped with a differential carrier made hollow, a connecting shaft (or a first rotary member) inserted in the differential carrier, and a hub (or a second rotary member) arranged in the differential carrier and made rotatable relative to the connecting shaft. The connecting shaft and the hub are arranged on an axis, and a bearing is fitted between the differential carrier and the connecting shaft.
On the differential carrier, on the other hand, there is fitted an annular electromagnet which is stopped in its rotation relative to the differential carrier by means of bolts. On the connecting shaft, moreover, there is fixed a cylindrical side wall to set a predetermined air gap between the side wall and the electromagnet. A drum is jointed to the outer circumference of the side wall, and a pilot clutch and a main clutch are arranged between the drum and the hub.
The pilot clutch is equipped with a clutch disc splined in the inner circumference of the drum, a cam member fitted axially movably on the outer circumference of the hub, a clutch plate splined in the outer circumference of the cam member, and an armature to be attracted toward the side wall by an electromagnetic force. On the other hand, the main clutch is equipped with a clutch disc splined in the inner circumference of the drum, and a clutch plate splined in the flange of the hub.
Between the cam member and the main clutch, moreover, there is arranged an axially movable push member. Between the cam member and the push member, still moreover, here are fitted balls. On the other hand, a drive pinion shaft is jointed to the hub, and the drive pinion shaft is jointed to the differential constructed by the gear mechanism.
According to the driving force transmission system thus constructed, when no electric current is fed to the electromagnet, the pilot clutch is released so that the torque of the connecting shaft is not transmitted to the hub. When the electric current is fed to the electromagnet, on the other hand, the magnetic flux passes through the side wall and the armature so that the armature is attracted toward the side wall by the electromagnetic force.
Then, the pilot clutch is applied to rotate the cam member, and this rotation is transmitted to the balls so that the push member is activated in the axial direction to apply the main clutch thereby to transmit the torque of the connecting shaft to the hub. The torque thus transmitted to the hub is transmitted through the drive pinion shaft, the differential and axles to the wheels.
On the other hand, the differential carrier is filled in its internal space with oil for lubricating and cooling the pilot clutch, the main clutch and the differential.
Here, in the pilot clutch or the main clutch, the torque is transmitted by the frictional force between the surfaces of the clutch disc and the clutch plate. It is, therefore, preferable to select the oil which can keep the wear resistance, the oil cutting property or the judder resistance of the clutch disc and the clutch plate satisfactory. In the differential, on the other hand, the torque is transmitted and differentiated by the meshing resistance of the gears. It is, therefore, preferable to select the oil which is low in the fluid point, and is excellent in the heat resistance and oxidation stability and load resistance.
In the driving force transmission system described in the aforementioned publication, however, the pilot clutch, the main clutch and the differential are arranged in a common space of the differential carrier. This makes it difficult to employ the oil which is suited individually for the pilot clutch, the main clutch and the differential. As a result, the active characteristics of the pilot clutch and the main clutch may be degraded to lower the transmission function of the driving force.
Moreover, the oil, as confined in the differential carrier, may wet the electromagnet to make the magnetic permeability of a magnetic circuit heterogeneous and to lower the transmission function of the clutch mechanism for the driving force. Still moreover, a foreign substance such as wear powder, as produced at the side of the differential, may enter the clearance between the clutch disc and the clutch plate to wear or break the clutch mechanism thereby to lower the durability or the transmission function of the driving force.
A main object of the invention is to provide a driving force transmission system capable of using the oil suited for the action characteristics of a clutch mechanism and sealing the clutch mechanism to be controlled by an electromagnet, from another mechanism.
Another object of the invention is to improve the accuracy of a gap to be formed between an electromagnet and a magnetic member.
Still another object of the invention is to reduce the number of parts of the driving force transmission system.
Still another object of the invention is to facilitate the handling of an electric wire for energizing the electromagnet.
Still another object of the invention is to improve the positioning accuracy of a first rotary member in the radial direction.
Still another object of the invention is to make it possible to mount the driving force transmission system on a vehicle such that it is arranged in a longitudinal intermediate portion of the propeller shaft.
Still another, object of the invention is to prevent the vibration at the vehicle body side from being transmitted to the electromagnet.
Still another object of the invention is to make it possible to mount the driving force transmission system on the vehicle without any special case and to arrange the same without modifying the transfer or differential.
Still another object of the invention is to suppress the entrance of a foreign substance into an electromagnet housing chamber.
Still another object of the invention is to improve the durability of a clutch mechanism.
Still another object of the invention is to facilitate the positioning of an annular electromagnet and a casing relative to each other in the circumferential direction.
Still another object of the invention is to suppress the plastic deformation of a first rotary member or nuts when stud bolts are embedded in the first rotary member and when the nuts are fastened after a fitting member is attached.
Still another object of the invention is to enhance the action efficiency for the clutch mechanism of the driving force transmission system of this kind by preventing the leakage of a magnetic flux establishing a magnetic path and to improve the controllability of the electromagnet for the clutch mechanism by preventing the fluctuation of the magnetic flux density in the magnetic path.
Still another object of the invention is to reduce the weight of the driving force transmission system.
Still another object of the invention is to enhance the applying force for the clutch mechanism thereby to increase the torque to be transmitted between the first rotary member and the second rotary member.
Still another object of the invention is to promote the cut of an oil film to be formed between a clutch plate composing the clutch mechanism and an armature or magnetic member for clamping the clutch plate.
Still another object of the invention is to make the clutch mechanism compact.
Still another object of the invention is to retain a low coercive force of a magnetic path establishing member acting as a path for a magnetic flux, as established by energizing the electromagnet, and a high hardness in a predetermined portion of the magnetic path establishing member.
Still another object of the invention is to suppress the difference in the magnetic attraction of the electromagnet among the products by minimizing the width of a welded portion, into which the materials for a body portion and an annular portion composing the first rotary member are welded, at the welding time thereby to minimize the influence upon the magnetic flux density of the magnetic path to be established.
Still another object of the invention is to joint the body portion and the annular portion of the first rotary member by adopting no welding means.
Still another object of the invention is to improve the joint strength between the body portion and the annular portion.
Still another object of the invention is to improve the working efficiency of electromagnetic type control means for the clutch mechanism.
Still another object of the invention is to improve the control performance of the electromagnet control means for the clutch mechanism.
Still another object of the invention is to suppress the noise or vibration of the clutch mechanism and the rotational chattering of a cam mechanism for applying the clutch mechanism.
According to the invention, therefore, there is provided a driving force transmission system comprising: a clutch mechanism to be kept wet with oil; and control means including an electromagnet for controlling the applied state of the clutch mechanism, and the clutch mechanism and the oil are housed in an oil chamber made liquid-tight. As a result, the oil, which is excellent in the effects for keeping satisfactory the characteristics of the clutch mechanism such as the wear resistance, the oil cutting or the judder resistance, can be used independently of another lubricating oil so that the transmission function of the driving force is improved.
Moreover, the oil chamber and the surrounding space are isolated liquid-tight by an isolating mechanism so that the oil, as confined in the oil chamber, is hard to leak to the electromagnet. As a result, the magnetic permeability of the magnetic circuit, as made of the electromagnet, is kept constant to stabilize the applying force for the clutch mechanism and additionally the transmission function of the driving force.
Moreover, the oil chamber and the surrounding space are isolated liquid-tight by the isolating mechanism so that the foreign substance, as may be present in the space around the oil chamber, can be prevented from entering the oil chamber. As a result, the wear or damage of the clutch mechanism is prevented to improve the durability of the clutch mechanism and the transmission function of the driving force.
In the driving force transmission system of the invention, on the other hand, the electromagnet is fitted on a stationary member, and a first rotary member is supported by a bearing with respect to the electromagnet and is rotatably supported by another bearing with respect to the stationary member.
As a result, a gap to be formed between the electromagnet and the first rotary member is accurately sized to suppress the fluctuation in the magnitude of the electromagnetic force for actuating the clutch mechanism.
As a result, the applying force for the clutch mechanism, i.e., the torque capacity is easily controlled to improve the transmission function of the driving force to be mutually transmitted between the first rotary member and the second rotary member. On the other hand, the first bearing and the second bearing are so arranged in substantially identical positions as to overlap in the radial direction. As a result, the space for arranging the first bearing and the second bearing in the axial direction can be made as small as possible to reduce the size of the driving force transmission system in the axial direction.
In the driving force transmission system of the invention, a connector accompanying the electromagnet engages with the stationary member to fix the electromagnet in the circumferential direction. As a result, the number of parts is suppressed. When the electromagnet is fixed in the rotating direction, on the other hand, the connector comes into a predetermined position of the stationary member so that the electric wire is easily connected with the connector.
In the driving force transmission system of the invention, the electromagnet can be fitted on the stationary portion such as the vehicle body. By this construction, the driving force transmission system of the invention can be arranged in an intermediate portion of a propeller shaft of the vehicle. In this case, the noise or vibration can be suppressed by interposing an elastic member between the stationary portion and the driving force transmission system.
The driving force transmission system of the invention is equipped with not only the oil chamber and an electromagnet housing chamber housing the electromagnet, and this chamber is isolated liquid-tight from the surrounding chamber. Thus, it is possible to prevent a foreign substance, as may be present outside of the electromagnet housing chamber, from entering this chamber, a result, the foreign substance is hard to enter the air gap which is formed between the electromagnet and the magnetic member, to keep the magnetic permeability of the air gap at a constant level thereby to improve the driving force transmission function of the clutch mechanism.
Since the electromagnet housing chamber is formed adjacent to the oil chamber and filled with a cooling fluid, the heat, as generated by applying the clutch mechanism, is cooled with the cooling fluid so that the wear or breakage of the clutch mechanism is suppressed to improve the durability of the clutch mechanism. As a result, the torque transmission performance of the driving force transmission system is kept satisfactory.
In the driving force transmission system of the invention, the electromagnet is fitted in the opening of a casing through a positioning mechanism. Since the positioning mechanism is arranged to face the opening, the worker can observe the positioning mechanism visually from the outside of the casing trough the opening when the casing and the annular electromagnet are to be positioned in the circumferential direction on the axis. Moreover, when the annular electromagnet (or unit) and the casing are out of phase in the circumferential direction, this phase difference can be corrected into coincidence not by moving the electromagnet and the casing in the axial direction but only by rotating the electromagnet. As a result, the works of positioning the electromagnet and the casing in the circumferential direction can be performed easily and promptly to improve the assembly of the driving force transmission system.
The driving force transmission system of the invention is composed of a plurality of parts, and stud bolts are employed for fitting those parts. Each of these stud bolts has such threaded portions at its two end portions that their external diameters are set according to the strengths of the parts to be screwed thereon. As a result, the strength of the embedded side externally threaded portion and the strength of the nut side externally threaded portion can be suited for the strength of either the member to be fixed or the nut, so that the shearing stress to act on the fixed member or the threaded nut portion can be lightened to suppress its plastic deformation. On the other hand, the strength of the stud bolt is set by setting the external diameter of the embedded side externally threaded portion and the external diameter of the nut side externally threaded portion to different values. As a result, the axial length of the stud bolt can be suppressed to make contribution to the size reduction of the fixed member.
In the driving force transmission system of the invention, a magnetic path is established to circulate through a rear housing supporting the electromagnet, a friction clutch mechanism and the armature when an electromagnetic coil composing the electromagnet is energized, so that the armature is attracted by the magnetic induction. As a result, the armature applies the clutch mechanism frictionally so that the first and second rotary members are brought into a torque transmitting state by the frictional applying force thereby to transmit the torque according to the frictional applying force for the clutch mechanism between the first and second rotary members.
Thus, a front housing to be contacted by magnetic path establishing members including the rear housing, the clutch mechanism and the armature is made of a non-magnetic material. As a result, the magnetic flux forming the magnetic path is hard to leak from the front housing thereby to reduce no magnetic flux density. As a result, the working efficiency of the electromagnetic type control means for the clutch mechanism can be improved over that of the driving force transmission system of this type of the prior art.
In the driving force transmission system of the invention, the front housing is made of an aluminum alloy, and the rear housing is made of a magnetic material such as iron. Then, the first rotary member can be lightened to reduce the size of the driving force transmission system itself.
In the driving force transmission system of the invention, nut members are so screwed on the rear end portion of the rear housing as to move forward and backward thereby to fasten the front housing from the rear end side. This can eliminate the chattering, as might otherwise be caused by the screwing between the front housing and the rear housing, thereby to hold the air gap between a yoke and the rear housing always at a constant value.
As a result, the fluctuation, as might be caused by the fluctuation in the air gap, in the magnetic flux density is not caused to eliminate the fluctuation in the attraction for the armature. As a result, a stable frictional applying force is generated from the clutch mechanism to improve the controllability of the electromagnetic type control means for the clutch mechanism.
In the driving force transmission system of the invention, on the other hand, there are interposed between the first and second rotary members: a main clutch for transmitting, when frictionally applied, the torque between the two rotary members; a pilot clutch to be frictionally applied by the electromagnetic force generated by the electromagnet; and a cam mechanism interposed between the main clutch and the pilot clutch for converting the frictional applying force of the pilot clutch into a force for pushing the main clutch. As a result, the frictional applying force of the pilot clutch can be smoothly amplified and transmitted to the main clutch through the cam mechanism.
As a result, the main clutch can be sufficiently applied frictionally to raise the torque to be transmitted between the first and second rotary members thereby to improve the driving force transmitting characteristics of the driving force transmission system.
According to the driving force transmission system of the invention, when the electromagnet is energized, the magnetic path is established to circulate through the side wall, the clutch mechanism and the armature so that the armature is attracted toward the side wall by the magnetic induction. As a result, the armature pushes the clutch plate into frictional engagement to connect the two rotary members in a torque transmitting state so that the torque according to the frictional applying force is transmitted between the two rotary members.
Moreover, the clutch plate, as confronting the armature, of the clutch mechanism is so constructed as to rotate integrally with the armature, and an oil film is formed in the clearance between the confronting faces of the clutch plate and the armature. However, the cutting of this oil film is promoted by oil film cut promoting means which is formed on at least one of the confronting faces of the clutch plate and the armature. This suppresses the drop, as might otherwise be caused by the formation of the oil film, in the action responsiveness of the clutch mechanism.
In the driving force transmission system of the invention, the clutch plate, as confronting the side wall of the first rotary member, of the clutch mechanism is made rotatable integrally with that side wall. Then, an oil film is formed in the clearance between the confronting faces of the clutch plate and the side wall. However, the oil film cutting is promoted by the oil film cut promoting means which is formed on at least one of the confronting faces of the clutch plate and the side wall. This suppresses the drop, as might otherwise be caused by the formation of the oil film, in the action responsiveness of the clutch mechanism.
Here, in the driving force transmission system of the invention, the clutch plate, as confronting the armature, in the clutch mechanism is made rotatable integrally with the armature, and the clutch plate, as confronting the side wall of the first rotary member, in the clutch mechanism is made rotatable integrally with the side wall. In this case, oil film cut promoting means is provided on at least one of the confronting faces of the clutch plate and the armature and on at least one of the confronting faces of the clutch plate and the side wall. As a result, the oil film cutting is promoted between the clutch plate and the armature and between the clutch plate and the side wall, so that the reduction, as might otherwise be caused by the formation of the oil film, in the action responsiveness of the clutch mechanism is more effectively prevented.
In the driving force transmission system of the invention, the clutch plate, as confronting the armature, of the clutch mechanism is made rotatable relative to the armature thereby to form an oil film in the clearance between the confronting faces of the clutch plate and the armature. However, the oil film cutting is promoted by oil film cut promoting means which is formed on at least one of the confronting faces of the clutch plate and the armature. This suppresses the reduction, as might otherwise be caused by the formation of the oil film, in the action responsiveness of the clutch mechanism.
In this case, the armature can function as one clutch plate of the clutch mechanism. As a result, the clutch mechanism can be made compact while retaining a predetermined function.
In the driving force transmission system of the invention, the clutch plate, as confronting the side wall of the first rotary member, in the clutch mechanism and the side wall are made rotatable relative to each other. Then, an oil film is formed in the clearance between the confronting faces of the clutch plate and the armature. However, the oil film cutting is promoted by oil film cut promoting means which is formed on at least one of the confronting faces of the clutch plate and the side wall. This suppresses the reduction, as might otherwise be caused by the formation of the oil film, in the action responsiveness of the clutch mechanism.
In this case, the side wall of the first rotary member can function as one clutch plate of the clutch mechanism. As a result, the clutch mechanism can be made compact while retaining a predetermined function.
In the driving force transmission system of the invention, the clutch plate, as confronting the armature, in the clutch mechanism is made rotatable relative to the armature, and the clutch plate, as confronting the side wall of the first rotary member, in the clutch mechanism and the side wall are made rotatable relative to each other. In this case, oil film cut promoting means is fitted on at least one of the confronting faces of the clutch plate and the armature and on at least one of the confronting faces of the clutch plate and the side wall.
Thus, the oil film cutting is promoted between the clutch plate and the armature and between the clutch plate and the side wall. As a result, the reduction, as caused by the formation of the oil film, in the action responsiveness of the clutch mechanism can be more effectively prevented, and the clutch mechanism can be made more compact.
The driving force transmission system of the invention is equipped, between the two rotary members, with: the main clutch for transmitting, when frictionally applied, the torque between the two rotary members; the electromagnetic type pilot clutch to be frictionally applied when energized; and the cam mechanism interposed between the main clutch and the pilot clutch for converting the frictional applying force for the pilot clutch into a force for pushing the main clutch. As a result, the functional applying force for the pilot clutch can be smoothly amplified and transmitted to the main clutch through the cam mechanism.
As a result, the main clutch can be forcibly applied frictionally to raise the torque to be transmitted between the two rotary members thereby to improve the driving force transmitting characteristics of the driving force transmission system.
In the driving force transmission system of the invention, when the electromagnet is energized, the magnetic path is formed to circulate through the side wall of the first rotary member, the clutch mechanism and the armature so that the armature is attracted toward the side wall by the magnetic induction. As a result, the armature applies the clutch mechanism frictionally so that the two rotary members are connected to transmit the torque by the functional applying force thereby to transmit the torque according to the frictional applying force for the clutch mechanism between the two rotary members.
Here, the magnetic path establishing members for establishing the magnetic path, when the electromagnet is energized, between the electromagnet and the armature are made of a low-carbon magnetic material, and the sliding portions of the magnetic path establishing members have highly hard surfaces. As a result, the magnetic path establishing members have a high magnetic permeability as a whole and a low coercive force, and have hard surfaces only at the sliding portions requiring the high hardness so that they are excellent in heat resistance and wear resistance.
As a result, it is possible to retain not only the low coercive force of the magnetic path establishing members but also the high hardness of the necessary portions. When the feed of the electric current to the electromagnet is interrupted, the magnetic path, as established in the magnetic path establishing members, promptly disappears to cause no delay in response to the interruption of the magnetic path. As a result, as soon as the current feed to the electromagnet is interrupted, the clutch mechanism interrupts its action thereby to interrupt the torque transmission between the two rotary members.
According to the driving force transmission system of the invention, the sliding portions of the magnetic path establishing members are given the highly hard surfaces by a surface hardening treatment. This surface hardening treatment to be applied to the sliding portions of the magnetic path establishing members include a carburizing treatment and a quenching treatment. The surfaces can be easily hardened either by carburizing and quenching only the surfaces of the sliding portions of the magnetic path establishing members or by carburizing the whole surfaces of the magnetic path establishing members, machining the carbulized surface portions excepting the sliding portions of the magnetic path establishing members and quenching the portions left unmachined.
In the driving force transmission system of the invention, the magnetic path establishing members are exemplified by the side wall of the first rotary member. This first rotary member is constructed of a bottomed cylindrical front housing made of a non-magnetic material, and a rear housing screwed on the rear end opening of the front housing to cover the rear end opening and made of a magnetic material. The rear housing constructs the side wall of the first rotary member. As a result, only the sliding portions can be easily subjected to the surface hardening treatment if the rear housing can be made to have a high magnetic permeability and a low coercive force.
The driving force transmission system of the invention is equipped, between the two rotary members, with the main clutch for transmitting, when frictionally applied, the torque between those rotary members, the electromagnetic type pilot clutch to be frictionally applied when energized, and the cam mechanism interposed between the main clutch and the pilot clutch for converting the frictional applying force for the pilot clutch into the force for pushing the main clutch. As a result, the frictional applying force for the pilot clutch can be smoothly amplified and transmitted to the main clutch through the cam mechanism.
As a result, the main clutch can be sufficiently applied frictionally to raise the transmission torque between the two rotary members thereby to improve the driving force transmitting characteristics of the driving force transmission system.
In the driving force transmission system of the invention, when the electromagnet is energized, the magnetic path is established so that the clutch mechanism is frictionally applied by the, magnetic induction. By this frictional applying force, the two rotary members are connected to transmit the torque so that the torque according to the frictional applying force for the clutch mechanism is transmitted between the two rotary members.
Moreover, the first rotary member is equipped with the front housing of a non-magnetic material and the rear housing, and the rear housing is composed of a body portion made of a magnetic material, and an annular portion made of a non-magnetic material and fitted on the radially intermediate portion of the body portion. The body portion and the annular portion are jointed by the electron-beam welding method.
According to this electron-beam welding method, the welded portion in which the two materials making the body portion and the annular portion are welded into each other, is extended narrow and deep so that the influences of the magnetic permeability upon the rear housing can be reduced. As a result, it is possible to suppress the difference in the magnetic attraction of the electromagnet among the products of the driving force transmission system and to retain the welding depth of the welded portions sufficiently thereby to improve the joint strength between the body portion and the annular portion.
In the driving force transmission system of the invention, the first rotary member is equipped with the front housing of a non-magnetic material and the rear housing, and the rear housing is composed of a body portion made of a magnetic material, and an annular portion made of a non-magnetic material and fitted on the radially intermediate portion of the body portion. Moreover, the annular portion is formed into a conical cylinder and is jointed to the body portion by fitting it in the conical annular hole formed in the body portion.
Thus, the joint of the annular portion, as composing the rear housing, to the body portion is strong, and no welding means need be adopted for jointing the annular portion and the body portion. As a result, the influences, as caused from the welded portion, of the magnetic permeability can be eliminated to suppress the difference in the magnetic attraction of the electromagnet among the products of the driving force transmission system. Moreover, the welding means can be omitted to lower the production cost.
According to the driving force transmission system of the invention, when the active force is applied for urging the annular portion of the rear housing to the body portion in the axial direction, the body portion is fitted to bite in a wedge shape into the annular portion. As a result, the joint strength of the annular portion to the body portion is further enhanced.
According to the driving force transmission system of the invention, the electromagnetic type control means for applying the clutch mechanism frictionally is equipped with the electromagnet positioned outside of the front housing and confronting one side of the clutch mechanism, as positioned in the front housing, through the rear housing, and the armature positioned in the front housing at the other side of the clutch mechanism and adapted to be attracted in the axial direction, when the coil of the electromagnet is energized, to push the clutch mechanism. Moreover, the front housing to be contacted by the clutch mechanism and the armature is made of a non-magnetic material. As a result, the magnetic flux establishing the magnetic path is hard to leak from the front housing so that it will not reduce the magnetic flux density. As a result, the working efficiency of the electromagnetic control means for the clutch mechanism can be improved over that of the driving force transmission system of this kind of the prior art.
According to the driving force transmission system of the invention, the front housing is made of an aluminum alloy so that the first rotary member can be lightened to reduce the weight of the driving force transmission system itself.
According to the driving force transmission system of the invention, the nut members are so screwed on the rear end portion of the rear housing as to move forward and backward thereby to fasten the front housing from the rear end side. As a result, it is possible to eliminate the chattering, as might otherwise be caused by the screwing between the front housing and the rear housing, and to retain the air gap to be formed by the electromagnet, always at a constant value. As a result, the fluctuation, as might otherwise be caused by the fluctuation in the air gap, is eliminated to eliminate the fluctuation in the attraction for the armature. In the clutch mechanism, therefore, the frictional applying force is stabilized to improve the control performance of the electromagnetic type control means for the clutch mechanism.
The driving force transmission system of the invention is equipped, between the two rotary members, with the main clutch for transmitting, when functionally applied, the torque between the two rotary members, the electromagnetic type pilot clutch to be functionally applied when energized, and the cam mechanism interposed between the main clutch and the pilot clutch for converting the frictional applying force for the pilot clutch into the force for pushing the main clutch. As a result, the frictional applying force for the pilot clutch can be smoothly amplified and transmitted to the main clutch through the cam mechanism. As a result, the main clutch can be sufficiently applied frictionally to increase the transmission torque between the two rotary members thereby to improve the driving power transmitting characteristics of the driving force transmission system.
According to the driving force transmission system of the invention, when a coil composing the pilot mechanism is inactive, the armature is inactive to activate neither the two cam mechanisms nor the clutch mechanism so that no torque transmission is performed between the first rotary member and the second rotary member.
When the coil composing the pilot mechanism is energized, on the other hand, it attaches and moves the armature in the axial direction. This moving force is converted by the first cam mechanism into a rotational force, which is converted by the second cam mechanism into a force for urging the clutch mechanism in the axial direction. As a result, the clutch mechanism is frictionally applied to transmit the torque between the first and second rotary members. In this case, the frictional applying force for the clutch mechanism rises in proportion to the flow of an electric current to be fed to the coil, so that the torque to be transmitted between the first and second rotary members rises in proportion to the increase in the flow of the current to be fed to the coil.
Here, the driving force transmission system is constructed such that the force for moving the armature composing the pilot mechanism in the axial direction is converted by the first cam mechanism into a rotational force, and such that this rotational force is converted by the second cam mechanism into a force for urging the clutch mechanism in the axial direction. This makes it unnecessary for the pilot mechanism to generate the frictional applying force. As a result, there can be adopted a pilot mechanism which is composed of the coil and the armature to be attracted, when the coil is energized, to move in the axial direction but is not equipped with the frictional clutch. As a result, it is possible to prevent the noises or vibration in the pilot mechanism.
In the driving force transmission system, on the other hand, the moving direction of the armature is always in the same axial direction no matter whether the directions of the relative rotations of the first rotary member and the second rotary member might be forward or backward. As a result, the action directions of the first cam mechanism and the second cam mechanism are unchanged so that the increase in the chattering of those cams in the rotational direction can be suppressed.
According to the driving force transmission system of the invention, the pilot mechanism is constructed of the coil and the armature to be attracted, when the coil is energized, to move in the axial direction. The armature is made to act as a first cam member of the first cam mechanism, whereas a second cam member of the first cam mechanism is made to act as the first cam member of the second cam mechanism. As a result, all the mechanisms including the pilot mechanism, the first cam mechanism and the second cam mechanism can be made compact to reduce the size of the driving force transmission system.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.